haskell: additional test cases for phone number exercise
Merge pull request #864 from mjhoy/haskell-phone-number-cases

haskell: additional test cases for phone number exercise
Prefer recent exercises in random work

It's more likely that there are fewer people nitpicking on the recent
exercises.

This does not loop through multiple languages, so there's a chance that
you will end up with no suggestion. This will be fixed in a later
commit.

Also, this is a hack. There are no tests. This will also be fixed in
said later commit.
Randomize language in `random_work`.

Random work will now pull the most recent exercise for any of
the languages that you've completed exercises in.

Still a hack.
rust rna-transcription - rust 0.8 no longer has map_chars, use replace instead
rust - check exercises automatically with travis (rust 0.8)
rust - word-count exercise